It's the same as the KA50 S-8 illumination rockets. You need to fire them at roughy 15 degrees up angle, they travel roughly 7km and will ignite, illuminating the ground below.
If you shoot them straight and level they'll just bury themselves in the ground and be destroyed.
Come to a hover (or be really good at math at speed), pitch the nose up roughly 15 degrees and launch a salvo. Wait approximately 30 seconds (it's the burntime of the flare) and launch another salvo keeping the area illuminated, again, 15 degrees nose up.